louise, try this,To perform a manual network roam on anAndroid device,go to the Settings menu,select Wireless and Networks, then,mobile networks, then,network operators,search for networks,a list of available networks will be displayedafter a short while.

Now select any network that is not giffgaff or02 (orange/Vodafone etc.)After a few moments you willsee "No Network Service" on the display.

Now go back and select giffgaff or 02 andchange the selection back to Automatic